How to select hidden children?
The short answer is, selecting them is not possible with Blender (at the moment?), since (viewport) hidden / disabled objects are treated like &quot;Disable Selection&quot; is turned on. The solution would be to use a workaround and depending on what you want to do. The good thing is, if you want to translate those hidden objects and they are parented to a visible object, they will perform the translation with their parent although they are hidden.
If you want to select all objects in a collection to duplicate them, instead of using RMB+Right-click &gt; Select Objects try RMB+Right-click &gt; Duplicate Collection.
This duplicates the collection with all objects, even those that are hidden (note: the option Hide in Viewport will be disabled, but the option Disable in Viewport  will keep its setting).
If you want to translate complete collections with hidden objects, the easiest way would be to add an empty to this collection, select all other objects in the Outliner and parent them to the empty by dragging them onto it with Shift+LMB.
To parent one object A with a hierarchy including children that are &quot;Disabled in Viewport&quot; to another object B, simply drag object A with Shift+LMB onto object B in the Outliner.